Fluid accumulator

ABSTRACT

This invention relates to a fluid accumulator comprising a wall ( 2 ) encompassing a reservoir ( 1 ) for receiving the fluid, part of the wall being elastically deformable. The wall ( 2 ) of the fluid accumulator comprises a first wall portion ( 2 A) that is made of a first elastically deformable composite, with fibrous reinforcement material applied in a first density, and a second wall portion ( 2 B) that is made of a second composite with fibrous reinforcement material applied in a second density and an elastic deformability that is the same as or different from the elastic deformability of the first wall portion, the density of the fibrous reinfrocement material in the first and second wall portion ( 2 A,  2 B) being different.

The invention relates to a fluid accumulator comprising a reservoirencompassed by a wall, part of the wall being elastically deformable, asdescribed in the preamble of the first claim.

From EP-A-197.911 a pneumatic hammer drill is known, which comprises ahydraulic accumulator in the form of a cylinder surrounding a coaxialpiston over part of its height. The cylinder is made of an elastic glassfibre reinforced epoxy resin, that provides the cylinder with therequired resilient features and the accumulation capacity resultingthere from.

From GB-A-2.134.984 a pressure vessel is known, for example for use ashydropneumatic accumulator, comprising a housing and a reservoircontaining the pressure medium provided in the housing. Thedouble-walled housing provides mechanical strength to the pressurevessel. The reservoir fitted in the housing is made of an elastomer andis provided to receive a gas. The space between the reservoir and thehousing is provided to receive a liquid. Increasing the gas pressure inthe reservoir, causes the reservoir to expand and liquid to be pressedout of the housing. The housing is made of a lining to which a fibrousreinforcement is applied.

However, for the hydropneumatic accumulator known from GB-A-2.134.984,the capacity of the pressure reservoir is determined by the volume ofthe housing.

U.S. Pat. No. 4,714,094 describes a gas-oil pressure accumulator havinga cylindrical body reinforced by an envelope of a load-bearing compositematerial. A piston slideable in the cyclindrical body separates thehydraulic oil chamber from the pressurized gas chamber. The accumulatordescribed in U.S. Pat. No. 4,714,094 is used as emergency unit inflight, and is able to supply a sufficient quantity of hydraulic oil aslong as the hydraulic oil is kept under pressure by the pressurized gas.This type of accumulator is operated under high gas pressure, andtherefore has a heavily reinforced cylindrical structure. Thecylindrical wall of the accumulator described in U.S. Pat. No. 4,714,094is essentially undeformable under load. Moreover the pressurized gaschamber has limited extensibility and is not able to contain a variableamount of gas, the amount of gas being dictated by the compressibilityof the gas used.

Other known accumulators are similar to, for example, expansion vesselsfor central heating and consist of a vessel that is divided into twoparts by a membrane. At one side of the membrane a gas under pressure iscontained. The space at the other side forms said closed reservoir forthe fluid, the membrane forming the elastically deformable wall portion.The construction of these accumulators is relatively expensive. Inaddition, the vessel may rust and the membrane may lose its elasticityor display leaks over time, causing the life span of these accumulatorsto be limited.

It is the aim of the present invention to provide a fluid accumulator,that can be manufactured relatively easily and that possesses a longlife span.

This aim is reached according to the invention with the technicalfeatures of the characterizing part of the first claim.

The fluid accumulator of this invention contains a reservoir encompassedby a wall for receiving the fluid, at least a portion of the wall beingelastically deformable. In order to allow pressure buildup the reservoiris closed or closable. The wall comprises a first wall portion made of afirst elastically deformable composite, that is preferably flexible, andthat is provided to elongate under pressure. The fibrous reinforcementmaterial is applied in a first density. The fluid accumulator furthercomprises a second wall portion made of a second composite with fibrousreinforcement material applied in a second density and having an elasticdeformability and expansibility that is equal to or differs from theelastic deformability of the first wall portion. The density of thefibrous reinforcement material in the first and second wall portion (2A,2B) is different.

The density of the fibrous reinforcement material in the first andsecond wall portion is adjusted to the desired expansibility of the wallportion in question and is lower in the wall portion with increasedexpansibility, and higher in the wall portion with lower expansibility.

As a result of expansion or transformation of the elastically deformablewall portion this accumulator can contain a variable amount of fluid,usually gas or liquid. Such accumulators may be part of a pressurecylinder or may be connected to a pressure cylinder, for example apressure cylinder of a hydraulic suspension, to collect the liquid thatis pressed out of the cylinder by the piston or to press this liquidback to the cylinder when the piston returns to its starting position.

The first expandable wall portion is preferably only part of a wall orcylinder shell.

The first expandable wall portion of the accumulator can for example bepart of a cylinder with a closed end in which a piston is movable to andfrom the closed end, between a minimum and a maximum inserted position.In that case the first wall portion preferably extends over the distancebetween the closed end and the maximum inserted position of the piston.

The fluid accumulator described higher is suitable for use in ahydraulic or pneumatic suspension with built-in accumulator orcompensator, a shock absorber, a hydraulic cylinder for dampeningmotions etc.

The fibrous reinforcement material used in the first wall portion can bethe same as or different from the fibrous reinforcement material used inthe second wall portion. The fibrous reinforcement material itself maydisplay a greater or smaller reversible elasticity. Expansion of thefirst wall portion can take place with or without stretching the fibrousreinforcement material. Elasticity of the fibrous reinforcement materialcan be obtained by applying the fibres in one or several previouslydetermined directions. In practice, this is obtained by positioning thereinforcement fibres at an angle of less than 90° with respect to thelongitudinal axis of the reservoir.

The expansibility of the first and second wall portions can be furthercontrolled by orientating the fibres in the first wall portion at afirst angle with respect to the longitudinal axis, and by orientatingthe fibres in the second wall portion at a second, different, angle withrespect to the longitudinal axis

The nature of the used fibrous reinforcement material is not critical tothe invention and will usually be selected by the man skilled in the arttaking account of the desired application. Suitable fibrousreinforcement materials are among others, metallic fibres, mineralfibres, for example glass fibres, carbon fibres, cotton fibres, flaxetc; synthetic fibres for example made of polyester, polypropene,polyethylene, polyamid or mixtures of two or several of said materials.However, due to its high elongation to break ratio a polyester fibre ispreferred. The form in which the fibrous reinforcement material is usedwill usually be adjusted by the person skilled in the art to the desiredapplication in view of the expected elasticity and pressure resistance.For this, use can be made of a mat or tissue or a non-woven material, oftwined or twisted fibres in order to provide improved elongation tobreak.

The fibrous reinforcement material used in the first and second wallportion may be identical or different, but is preferably different. Forinstance, in the first wall portion with increased expansibility use ismade of glass fibres while in the second wall portion with lowerexpansibility preferably fibres with greater stiffness and strength, forexample carbon fibres or polyester fibres, are used.

The nature of the plastic used in the fluid accumulator is not criticalto the invention and will usually be adjusted by the man skilled in theart to the desired application. Suitable plastics are among othersthermoplastics or a mixture of two or more thermoplastics, athermosetting resin or a mixture of two or more thermosetters, anelastomer or a mixture of two or more elastomers, or a mixture of two ormore thermoplastics, thermosetting resins or elastomers. However,elastomers and thermoplastics are preferred because of their flexibilityand the optimal reversible character of their expansibility.

Examples of suitable thermoplastics are amorphous, crystalline andsemi-crystalline materials. Examples of suitable thermoplastics are oneor more materials of the group of polyurethane, polyethylene,polypropylene, ethylene-propylene copolymers, polybutadiene rubber or amixture of two or more of these substances. Examples of suitablethermosetting resins are polyurethane, vinylester resins, unsaturatedpolyester resins, or a mixture, of two or more of these materials.Examples of suitable elastomers are polyurethane, polypropylene,ethylene-propylene copolymers, polybutadiene rubber. These materials maybe amorphous crystalline as well as semi-crystalline, depending on thedesired application.

Preferably use is made of a vinylester resin or of a polyurethaneelastomer.

The first and second wall portion may be made of the same plastic, butare preferably made of different plastics in order to enable bettercontrol of the expansibility of the individual wall portions.

By adjusting the nature of the fibrous reinforcement material and theplastic in the first and second wall portion to the desiredexpansibility, optimal control of the expansibility of each of the firstand second wall portions can be provided.

The invention also relates to a method for manufacturing the previouslydescribed fluid accumulator.

According to this method a cylinder shell comprising a fluid reservoirencompassed by a wall, is provided with a first expandable wall portionmade of a fibrous reinforced composite and a different plastic material,fibrous reinforcement material or both, are used at the position wherethe first expandable wall portion transfers into the second expandablewall portion that displays reduced or hardly any expansibility, and thiscylinder shell is closed by end walls.

One of the end walls can be manufactured as a piston and slidablymounted in the cylinder shell, the expandable portion of the cylindershell being fitted between a fixed end wall and the piston in maximuminserted position.

The wall of the fluid accumulator can be manufactured in several ways.The most suitable method will be selected by the person skilled in theart in view of the desired application.

It is possible, for instance, to manufacture the wall by “filamentwinding”. The fixed end wall or end walls can be manufactured by“filament winding” as well, in one piece with the cylinder shell.Filament winding is a technique according to which fibres or fibrestrands are soaked in plastic and wound on a rotating mandrel orcylinder in the desired form, after which the plastic sets.

In another embodiment the cylinder shell is manufactured by “braiding”,a technique according to which a woven sleeve soaked in plastic, iscured usually in a mould in a vacuum. “Braiding is described amongothers in the American patent publications 260,143 and U.S. Pat. No.4,326,905.

In yet other embodiments the cylinder shell is manufactured by acombination of “filament winding” and “pultrusion”, i.e. by theso-called “pullwinding” or by a combination of, “braiding” and“pultrusion”. Pultrusion is a commonly known technique, according towhich wires or mats are soaked with curable resin that are pulledthrough a mould, after which the resin is allowed to cure. “Pulwinding”is a variant of pultrusion in which one or more layers of reinforcementfibres are wound, which layers are soaked in plastic prior to or afterthe winding. Next the whole is pulled through an extrusion machine,after which the plastic cures. In these embodiments with “pultrusion”the fixed end of the cylinder must be manufactured separately,preferably also from composite material, possibly from elasticallydeformable plastic.

The invention is further clarified by the attached figures and figuredescription, in which

FIG. 1 displays a schematic cross section of a fluid accumulatoraccording to the invention;

FIG. 2 displays a schematic cross section analogous to that of FIG. 1,but relating to another embodiment of the accumulator, namely assuspension.

The fluid accumulator, displayed in FIG. 1, comprises a reservoir 1 forreceiving the fluid, for example a gas, or a liquid. The reservoir issurrounded longitudinally by aside wall 2 and contains at opposite endsof the side wall first and second end walls 3 and 4. The reservoir, mayhave any desired shape, and can be, for example, cylinder-shaped orbeam-shaped or have any other shape depending on the desiredapplication.

The side wall 2 and the end walls 3 and 4 are made of a composite, i.e.a fibrous reinforced plastic.

The side wall 2 comprises a first expandable wall portion 2A. The firstwall portion is preferably made of an elastically deformable, reversiblyexpandable plastic material. The side wall 2 also comprises a secondwall portion 2B that displays reduced expansibility. The second wallportion can be made of the same plastic material, but will usually bemade of a plastic with reduced elastic transformability andexpansibility.

During the production process, for example by “filament winding”, theless expandable part is made of a plastic with reduced elasticity andtransformability and/or the fibres are applied in a greater density. Theflexibility and elasticity can also be controlled by executing thenon-expandable part 2B with a greater thickness than the firstexpandable part 2A. It is possible to control the elasticity by busing adifferent fibrous reinforcement material in the first and second wallportions. It is also possible, during the “filament winding”, to applythe fibres crosswise, at an angle of less than 90° with respect to theaxis of the reservoir 2 and to use a different winding method in thefirst and second part.

In another embodiment of the invention the entire wall of the reservoiris elastic.

The end walls 3 and 4 can be manufactured in a mould, from nonelastically deformable plastic, for example an epoxy resin or apolyester, provided with fibrous reinforcement material. Both theplastic and the fibrous reinforcement material may be the same as, ordifferent from the material of which the wall 2 of the reservoir ismade. The end walls may be attached to the wall 2 in several ways, forexample by means of gluing with an epoxy glue, or they may be part ofthem. This will usually depend on the manufacturing technique that isused.

However, in a variant one or both end walls 3 and 4 may also be made ofelastically deformable material, for example of a polyurethaneelastomer.

The end wall 3 may also be provided with a connection 5 for connecting asupply line 6.

In an alternative embodiment the cylinder shell 2, in one piece with theend walls, 3 and 4 or not, is made by “braiding” in stead of “filamentwinding”. In a further alternative embodiment the cylinder shell 2 ismanufactured by a combination of filament winding and pultrusion, i.e.by the so-called pullwinding or by a combination of braiding andpultrusion. In these variants the end walls 3 and 4 are usually madeseparately.

FIG. 2 shows the fluid accumulator described above, that is used in anhydraulic suspension with built-in accumulator. In this hydraulicsuspension the end wall 3 is replaced by a piston 7 that is movable toand from the opposite end wall 4. A piston rod 8 is fixed to piston 7.In this embodiment the non expandable wall portion 2B is executed longerand extends over the full travel of the piston 7. The expandable wallportion 2A is located between the end wall 4 and the piston 7 in maximuminserted position.

The piston 7, if so desired in one piece with the piston rod 8, is madeof composite material in a mould, but it can also be made by filamentwinding or braiding.

The end of the cylinder shell 2 through which the piston rod 8 extendsoutward is open, or partly closed, for example by a wall 9 with openings10 that forms a guide for the piston rod 8. The wall 9 is preferablyalso made of composite material and glued to the cylinder shell 2 or ismade as a whole. With the cylinder shell 2 by “filament winding” or“braiding”.

When the piston rod 8 is pushed in, pressure is exerted on the fluid inthe reservoir 1 resulting in the expansion of the wall portion 2A of thecylinder shell. When piston 7 is pushed out, the pressure on the fluiddecreases and the expandable wall portion 2A returns to its originalform entirely or partially, depending on the pressure decrease.

The accumulator of this invention is suitable for use with various typesof fluids, for example water, oil or every other liquid, or a gas. Inthe last case the expansibility of the first wall portion 2A is subjectto less demands.

The suspension may be used in vehicles, as a shock absorber, or asdampener for absorbing shocks in machines or for tempering motion incranes.

The invention is in no way limited to the embodiment described above anddisplayed in the attached figures, but such fluid accumulator and methodfor manufacturing thereof can be realized in several variants withoutexceeding the scope of the invention.

1. A fluid accumulator comprising a closable reservoir for receiving thefluid under a working pressure, which is enclosed by a circumferentialside wall and a first and second end wall on opposite end parts of thecircumferential side wall, wherein the circumferential side wallcomprises in the longitudinal direction, a first circumferential wallportion made of a first elastically deformable composite material, whichis deformable under the action of the mean working pressure and a secondcircumferential wall portion made of a second composite material, whichis essentially undeformable under the action of the working pressure. 2.The fluid accumulator according to claim 1, characterized in that thefirst and second composite material comprise a fibrous reinforcementmaterial and in that the density of the fibrous reinforcement materialof the first composite material differs from the density of the fibrousreinforcement material of the second composite material.
 3. The fluidaccumulator according to claim 2, characterized in that the wall is madeentirely of a fibrous reinforced composite, the composite containing aplastic material and the plastic material of the first wall portionbeing an elastic plastic material, provided to elongate reversibly underpressure.
 4. The fluid accumulator according to claim 1, characterizedin that the composite material of the first wall portion contains afirst plastic and the second wall portion contains a second plasticmaterial that displays a different elastic deformability.
 5. The fluidaccumulator according to claim 1, characterized in that the first andsecond composite material comprise a fibrous reinforcement material andin that the fibers of the fibrous reinforcement material in the firstand second wall portion are orientated at different angles with respectto the longitudinal axis of the reservoir.
 6. The fluid accumulatoraccording to claim 5, characterized in that the angle is less than 90°.7. The fluid accumulator according to claim 1, characterized in that thefirst and second composite material comprise a fibrous reinforcementmaterial and in that the fibrous reinforcement material applied in thefirst wall portion are glass fibers.
 8. The fluid accumulator accordingto claim 1, characterized in that the first and second compositematerial comprise a fibrous reinforcement material and in that thefibrous reinforcement material applied in the second wall portion arecarbon fibers and/or polyester fibers and/or aramid fibers.
 9. The fluidaccumulator according to claim 1, characterized in that the first and/orsecond composite material comprises a vinylester resin.
 10. The fluidaccumulator according to claim 1, characterized in that the reservoir isenclosed by an essentially cylindrical side wall, an end wall and wallof piston, which piston is slidably mounted into the accumulator to moveto and from end wall, and that the first wall portion extends betweenthe end wall and the piston when in a position of maximum displacementin the direction of the end wall.
 11. The fluid accumulator according toclaim 10, characterized in that at least part of the piston comprises afiber-reinforced composite.
 12. The fluid accumulator according to claim1, characterized in that the wall essentially consists of compositematerial which has been manufactured by filament winding, braiding, acombination of filament winding and pultrusion, pullwinding, acombination of braiding and pultrusion.
 13. The fluid accumulatoraccording to claim 1, characterized in that the first and second wallportion essentially consist of composite material manufactured usingdifferent techniques.
 14. A hydraulic or pneumatic suspension withbuilt-in accumulator or compensator, a shock absorber or a hydrauliccylinder for dampening motions which comprises the fluid accumulatoraccording to claim 1.